late period, sometimes I feel lower abdominal twitching

Hi, I usually have a normal period... But I'm 18 days late. I took a test last week and it said negative. Still no sign of my period. I have a steady boyfriend for 5 years now, and we usually used the "pull out method" recently we started using protection. Should I be worried that I'm pregnant? I sometimes feel lower abdominal twitching. Plz help